In-situ Resource Utilization (ISRU) is going to be a critical technical component of any human expansion out into the solar system. Our first challenge with utilizing those resources, though, is finding them. We know how, at least in theory – send a probe to an asteroid, or a particular part of the Moon, and take a sample, maybe analyze that sample with some spectrographs, or send it back to Earth to be poked and prodded. The problem with this methodology is simple – it’s expensive. Sending dedicated probes to every near-Earth asteroid, or every potentially interesting site near a lunar base is prohibitively expensive. So a new NASA Institute for Advanced Concepts (NIAC) grant explores a different opportunity – using a single, relatively small spacecraft to visit multiple ISRU locations, and figure out their composition from tens of kilometers away.
To understand how, we have to talk about Raman spectroscopy. When you shoot a material with a laser, most of the light scatters back at the exact same wavelength. But a very small fraction of it will interact with the molecular bonds of the material it hits, shifting its energy in a way that is recognizable to the right software algorithm. By reading that shifted light, scientists can get a “molecular fingerprint” of whatever minerals are present in the material the laser just bounced off of.
We’ve even used Raman spectroscopy on space missions before. Perseverance has two instruments – SuperCam and SHERLOC, that can identify materials in the Martian dirt. But the rover has to be basically right on top of the rocks to get an accurate read. The new NIAC proposal, headed by Dr. Pablo Sobron Sanchez of the SETI Institute, proposes doing the same thing, from 30-50 km away and traveling at interplanetary speeds.
Fraser talks about in-situ resource utilization – the technology the Slingshot mission hopes to enable.
To be clear, the proposal, which is called the Interworld Slingshot, isn’t just a fancy Raman spectroscopy instrument – it’s an entire mission architecture. It envisions a 300-kg spacecraft, which would be roughly the size of a household refrigerator when packed up – and would neatly fit it into the “Discovery” class of mission.
It would be powered by solar panels and an efficient Solar Electric Propulsion (SEP) system, both of which must be optimized to fit in the 300-kg package. But really the important part of the mission architecture is captured in its name. In orbital dynamics, a “slingshot” happens when a probe uses the gravity of another body (such as a planet or a moon) to accelerate to speed unachievable by any conventional propulsion system we have access to today.
Utilizing a complex series of slingshots, the mission would embark on a three-part tour of the solar system. The first stop would be our own Moon, where the spectroscope would map water ice and ilmenite, a type of titanium-iron oxide that can be processed into oxygen for astronauts to breathe, and to use for rocket fuel.
Fraser talks about what we could potentially find on Mars to help us live off of it.
After visiting the Moon, the mission would next fly by a near-Earth asteroid, attempting to identify silicates, metals, and valuable organics like methane that could be of use to future space miners. For the final leg of the journey, the probe would settle into orbit around one of Mars’ moons – either Phobos or Deimos – while also mapping out volatiles that could make Mars’ companion useful as a future space gas station.
This all sounds great in theory, but the engineering novelty behind it is staggering. The whole idea is premised on using Raman spectroscopy, which is typically used at a distance of a few meters, at a distance of 10s of kilometers. Dr. Sobron Sanchez has some form in this area, successfully testing a “long-distance” spectrometer to the distance of a few hundred yards, but it’s still a far cry from what would be necessary given the vast distances between the probe and its targets as part of the mission.
That’s not to mention the other difficulty – speed. For Raman spectroscopy to work, the signals can’t be blurred, and the probe itself will be moving at a rapid pace past most of its targets, which is exactly what causes blur. To solve that requires some extreme signal processing as well as stabilization techniques from the physical hardware in order to have a chance of working.
But after all, this is a NIAC grant. They are supposed to be futuristic, cutting edge, and maybe practically impossible. If we don’t shoot for the Moon we’ll never land amongst the stars. Or next to a Martian moon all while scanning it for useful materials, as the case may be.
Learn More:
Pablo Sobron Sanchez – Interworld Slingshot Resource Surveys
UT – Demonstrating Lunar Surface Raman Spectroscopy with the Raman Cube Rover
UT – Rare Element Could Point the Way to Past Life on Mars
UT – Perseverance Finds a Wealth of Organic Materials on Mars
Andy has been interested in space exploration ever since reading Pale Blue Dot in middle school. An engineer by training, he likes to focus on the practical challenges of space exploration, whether that’s getting rid of perchlorates on Mars or making ultra-smooth mirrors to capture ever clearer data. When not writing or engineering things he can be found entertaining his four children, six cats, and two dogs, or running in circles to stay in shape.
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